1. Field of the Invention
The present invention relates to a wireless transmitter-receiver device in which electric power is selectively supplied from a battery to wireless circuits.
2. Description of Related Art
Recently, an automobile license plate on which a wireless device is mounted for wirelessly transmitting a license number and a vehicle identification number (a so-called smart plate) has been proposed. The wireless device is always exposed to water splash, sunshine or other hazardous atmosphere. Therefore, the wireless device including a battery for supplying power to wireless circuits has to be contained in a hermetically encapsulated casing. When the battery is contained in such a casing, it is impossible to connect or disconnect the battery to the wireless circuits (referred to as activation of the battery) from outside. Accordingly, the encapsulated battery has to be continuously kept activated after the wireless device is manufactured in a device manufacturer.
A considerably long period of time is required after the wireless device is manufactured until it is actually used. If the battery is continuously kept activated, battery power is consumed in vain. Usual processes in this period are as follows. The wireless device is inspected after completion of the manufacturing processes. The battery has to be activated for performing the inspection. Then, the wireless device is shipped to a license plate manufacturer to be mounted on the license plate. The battery has to be activated to store a vehicle identification number and a license number in a memory included in the wireless device. Then, the license plate on which the wireless device is mounted is sent to a place, such as a transportation authority, where the license plate is mounted on a vehicle. The battery has to be activated to store information regarding security or the like in the memory. Then, the vehicle is delivered to a user, and the wireless device is put into actual use. After that, the battery has to be continuously kept activated. However, it is not necessary to keep the battery activated in periods of transportation or waiting time between processes. Rather, it is most desirable to keep the battery inactivated to save battery power consumption.
Power saving of this sort is required not only in the wireless device for the license plate but in other devices which are put into actual use a considerably long time after they are manufactured.